Today, there are many radio and cellular access technologies and standards such as Global System for Mobile Communications (GSM)/General Packet Radio Service (GPRS), Wideband Code-Division Multiple Access (WCDMA)/High-Speed Packet Access (HSPA), Code-Division Multiple Access (CDMA)-based technologies, WiFi, Worldwide Interoperability for Microwave Access (WiMAX) and recently Long Term Evolution (LTE), to name a few. The technologies and standards have been developed during the last few decades, and it can be expected that the development will continue. Specifications are developed in organizations like 3rd-Generation Partnership Project (3GPP), 3rd-Generation Partnership Project 2 (3GPP2) and Institute of Electrical and Electronics Engineers (IEEE).
3GPP is responsible for the development and maintenance of GSM/GPRS, WCDMA/HSPA and LTE standards. This disclosure focuses primarily on the HSPA-evolution built on the WCDMA radio access, also called Universal Terrestrial Radio Access Network (UTRAN), and LTE, based on Orthogonal Frequency-Division Multiplexing (OFDM) and Single-Carrier Frequency-Division Multiple Access (SC-FDMA), which is also known as the Long Term Evolution of UTRAN, or Evolved Universal Terrestrial Radio Access Network (E-UTRAN). Detailed UTRAN radio access specifications are described in the 25-series of 3GPP specifications, while E-UTRAN specifications are found in the 36-series. LTE was introduced in 3GPP Release 8, but the development and future evolution of both HSPA and LTE continues in parallel in 3GPP Releases 9, 10 and so on.
Various frequency bands are typically allocated and/or sold by government organizations, such that an operator may “own” certain bands for a particular use. In some cases, government regulations may specify that the owner, i.e., the operator, should deploy a particular technology in a particular frequency band. In some cases, the operator may be able to choose what technology and standard to deploy in their spectrum provided the choices fulfill certain criteria set up by, for example, the International Telecommunications Union (ITU).
As a consequence of the fact that spectrum is a scarce resource, an operator may have the rights to deploy a new cellular access, such as LTE, in a limited spectrum, such as 20 MHz. However, the fact that the operator may have an existing customer base with existing terminals may prevent the operator from deploying only a single technology across the whole spectrum owned by the operator. This could be the case, for example, for an operator that has a large existing customer base with WCDMA/HSPA subscriptions using the UTRAN network, but who wants to deploy the most recent evolution, the Long Term Evolution (LTE) of UTRAN, also called E-UTRAN.
In this example, the operator may then have to divide the available bands between HSPA and LTE. At initial deployment of LTE, the operator may thus continue to use, for example, 10 MHz (corresponding to two WCDMA carriers) for HSPA and reserve 10 MHz for initial LTE deployment.
However, such partitioning of a scarce spectrum resource to different technologies has some undesired effects on performance. First, there is a direct correlation between the peak-rate that can be offered and the spectrum width that is used. Thus, limiting the bandwidth of both HSPA and LTE to 10 MHz in the example above will roughly limit the peak-rate offered to customers to one-half of that which could be supported if the entire spectrum was utilized for a single access technology. Assuming for the sake of illustration that each of the technologies can offer around 100 Mbps in 20 MHz, it will mean that the peak-rate will now be limited to around 50 Mbps in each of the technologies. Second, it may happen that the HSPA carriers are very loaded for some time after the newer technology is deployed, while the LTE carriers in the example only have a few users. Thus, there would be an imbalance between allocation and use, resulting in undesired congestion on the HSPA carriers and underutilization of the spectrum allocated to LTE. However, in order to offer a commercially acceptable bit-rate on the LTE carriers, it is still not possible to allocate, for example, only 5 MHz to LTE customers, since then the LTE evolution would not provide competitive performance in relation to HSPA.
Accordingly, there is a need for improved approaches to utilizing the limited spectrum resource while simultaneously deploying multiple radio access technologies.
In the published European patent application EP 2 203 001 A1, methods and apparatuses for adapting bandwidth usage in a cellular communication network are disclosed. A bandwidth assignment means assigns dynamically one portion of a bandwidth to one radio access technology and another portion of the bandwidth to another radio access technology based on the number of supportive mobile terminals and the level of traffic for the different radio access technologies. Such approach may compensate for relatively slowly varying use of the different radio access technologies. However, the available peak-rate will still be limited if not all the bandwidth may be utilized for one technology at a time. Moreover, fast variations in load for the different radio access technologies may be difficult to handle.
3GPP is currently progressing on a project called “IP Flow Mobility and seamless WLAN offload” (IFOM), the details of which are being captured in 3GPP TS 23.261. In this work, the idea is that a User Equipment (UE) can be simultaneously connected to Wireless Local Area Network (WLAN) and 3GPP accesses (such as HSPA or LTE), so that selected Internet Protocol (IP) flows can be routed over WLAN to offload the cellular access. However, in this approach each IP flow (e.g., a Transmission Control Protocol (TCP) connection) must take one or the other of the routes (i.e., either cellular or WLAN), and high peak rates can only be achieved if the UE is simultaneously using several IP flows that load both accesses evenly and simultaneously. Thus, the IFOM approach does not offer any benefits with regards to peak rates if a user downloads a single file or connects to one particular server via a single connection or flow.
Furthermore, since the connections over WLAN and the cellular access may exhibit different latencies, there is also a risk of severe re-ordering of packets. Thus, while IFOM provides a mechanism for offloading the cellular access, it does not offer a solution to the aforementioned problems related to peak rates in the scenario described above. Since the aggregation of different IP flows is performed above the radio access layers, it will mean that fast load-balancing between the access technologies is not possible, or at least, very demanding.
The mechanism used to setup IFOM is purely UE-based, and there is no coordination between the two accesses on radio network level, meaning the two access networks are not aware of that IFOM is used.
In the published international patent application WO 2007/078663 A2, a mobility middleware architecture for multiple radio access technology apparatuses is disclosed. Such middleware operates in a similar manner as in IFOM discussed above, and may provide a user with access to a Frequency Division Duplex (FDD) network, for example, simultaneously with access to a WLAN. Different data streams can then be directed to different radio access technologies. This may solve congestion problems if parallel data streams exist for a single user. However, in this case, the peak-rate will still be limited to the portion of the bandwidth that is assigned for each radio access technology.
Wireless communications using multiple radio access technologies simultaneously are disclosed in the published U.S. patent application publication US 2010/0062800 A1. A wireless device has a host controller unit that segments the uplink data stream and provides each of the segmented portions to either a first baseband module corresponding to a first radio access technology or a second baseband module corresponding to a second radio access technology. The segmented portions are combined again into a single data stream in a network entity after radio transmission using the two separate radio access technologies. Such approaches may solve both congestion and peak-rate limitations when being in continuous and non-mobile operation. However, there is no presented detailed strategy how to manage several issues such as initiation or mobility.